Setting "Field Level-security" to make email opt-out field visible

Changing Field Level Security for Leads' Email Opt Out

1. Click on "Your Name" | Setup | App Setup | Customize | Leads | Fields
2. Click on 'Email Opt Out' and then on the 'Set Field-Level Security' button
3. Locate your Profile and place a check in the 'Visible' box
4. Click Save

Changing Field Level Security for Contacts' Email Opt Out

1. Click on "Your Name" | Setup | App Setup | Customize | Contacts | Fields
2. Click on 'Email Opt Out' and then on the 'Set Field-Level Security' button
3. Locate your Profile and place a check in the 'Visible' box
4. Click Save 

Note: if you cannot find the 'Set Field-Level Security' button, make sure to click on the 'Email Opt Out' link and not on Edit to the left of it.